This project will investigate the feasibility of a highly automated, self-regulating ventilatory support system based on the servo-control technology. Two levels of servo control will be considered: 1) control of the instantaneous patterns of inspiratory airflow and airway pressure consistent with the patient's intrinsic respiratory drive (if any) and respiratory mechanics; and 2) control of the breath-to-breath ventilation for long-term regulation of the arterial blood gas levels. The first level of control is based on the concept of negative impedance ventilation which requires the instantaneous pressure applied at the airway to be porportional to either the airflow rate (negative resistance) or inspired volume (negative elastance). This innovative approach has the advantage of complete synchronization of the ventilator cycle with the patient's respiratory efforts, thereby allowing more effective human-machine interface. The technology is made possible by the advent of a fast-responding servo valve (Siemens-Elema) which allows rapid adjustment of the inspiratory pressure and airflow waveforms during mechanical ventilation. This sophisticated device, which is central to the implementation of the proposed negative impedance ventilation mode, has been made available to us through a donation from Siemens Corporation. We have employed the technique of negative resistance ventilation in preliminary study of ventilatory control mechanisms in normal exercising humans. The present study will evaluate its clinical applicability as a ventilatory support modality. The second level of servo control makes use of a low-cost, high-performance microprocessor as a digital controller. This offers flexibility in systems design and operation as well as the capability for multi-input multi-output data processing. The suitability of respired gas and lung mechanics monitoring as part of the feedback loop will be studied. System performance will first be tested with an artificial test lung (Michigan Instruments) which simulates the human respiratory mechanical system in normal and various disease states. Further evaluation will be obtained with clinical trials on both normal and COPD patients. The study will establish the practical feasibility of the proposed ventilatory mode and will lay the groundwork for the long-term evaluation of its efficacy.